This topic has been appearing in many forums across the net, most often linked to a short news article. So I have spent a bit of time trying to verify some of the claims.
Bonobos (clearly bi-sexual) and some Dolphins (again bi-sexual) aside, an oft used example is the Black Swan and it is connected to a higher survival rate for acquired eggs. This is only true when there are environmental factors, limited territory availability in suitable habitat. If the environmental stress factor is lifted, the success rates of hetero/homo Black swans is virtually equal.
From Wiki on black swans:
"Having access to more food the brood have up to ten times the survival rate of a brood with a heterosexual swan couple." What is often left out of the quote is the following first line from the next paragraph:
"This situation only holds true as long as a nest and/or a territory is in short supply."
What I have not been able to discover is whether these MM swan couplings are also based on female availability in that territory, during the time when these males are looking (being driven to) find a partner.
Another set of birds is being tossed about as examples of homosexuality are a couple of types of gull. This one I found particularly amusing:
"They found that on the Hawaiian island of Oahu, almost a third of the Laysan albatross population is raised by pairs of two females because of the shortage of males. Through these 'lesbian' unions, Laysan albatross are flourishing. Their existence had been dwindling before the adaptation was noticed."
Homosexual behaviour widespread in animals according to new study - Telegraph
So I googled Laysan albatross:
"This species is classified as Vulnerable owing to a projected rapid decline over three generations (84 years) based on declines in populations at Midway Atoll, French Frigate Shoals and Laysan Island in the late 1990s and early 2000s. More recent data indicate that the breeding population may have rebounded (perhaps because apparent changes in the breeding populations reflected large scale environmental conditions that affected the number of birds that returned to the colonies to nest rather than actual declines in the population). If so, this species would warrant downlisting to Near Threatened."
Laysan Albatross (Phoebastria immutabilis) - BirdLife species factsheet
How did it become vulnerable?
The Laysan Albatross, while a common species, has not yet recovered from the wide-scale hunting that happened in the early 1900s,[4] with feather hunters killing many hundreds of thousands, and wiping them out from Wake Island and Johnston Atoll.
Laysan Albatross - Wikipedia, the free encyclopedia
Now to the point:
"The population on Oahu has 59% females, probably as a result of female-biased recruitment to this relatively recently formed colony, and Young et al. suggest that the skewed sex ratio has driven the same-sex behavior, with a tendency toward social monogamy fostering its persistence."
http://www.faculty.ucr.edu/~mzuk/Zuk...one%20wild.pdf
Without looking beyond the telegraph article, one could come to the assumption that FF partnering is the cause of population rebound, rather than the FF partnering is a result of environmental stress (low male to female ratio)
Has low male to female ratios been tested? Well, yes, kinda. Several studies removed male chicks from populations and the results recorded higher FF pairings than in colonies which did not have this environmental factor (page 9):
http://beheco.oxfordjournals.org/cgi...nt/18/1/21.pdf
So with an environmental stress, we can increase the occurances of FF pairings. Do we consider an environmental stress factor a natural condition?
Another interesting snippet from a full article (rather than a snippet produced by a news site):
"In the dung fly Hydromyza livens, for example, males have been hypothesized to mount other males to deny them the opportunity to mate, thereby increasing the likelihood that the mounting male obtains more mating opportunities [24]. By contrast, in the viviparous Goodeid fish Girardinichthys multiradiatus, males sometimes display a dark, female-like ‘pregnancy’ spot around their vent. Subordinate males with dark spots attract fewer aggressive maneuvers by dominant males, who appear to mistake them for females and consequently court them [25]."
http://www.faculty.ucr.edu/~mzuk/Bai...0behaviour.pdf
Now is the above homosexual behavior? I think the dung fly example indicates a method to increase its own genetic survival (and further study is needed) before assigning 'homosexual', and the fish example seems clearly a heterosexual male being fooled by a female mimic (which seems to be a heterosexual), but this is not unlike some men who are aghast when they find out the female prostitute they picked up is really a transvestite. But often, these kinds of examples are used as 'evidence homosexuality is normal' in various news clippings.
Another mentioned insect (though maybe not in this thread) is the Dragonfly/damselfly (several species). What is often used as a 'possible' indication of homosexual behavior is markings on the males neck, which indicate it has been grasped during courtship.
Interesting tidbit of info I learned attending the Bug Festival in June was dragonflies have the ability to scoop out the sperm that has been deposited in the female and then cause the female to seek out this males sperm. This is why the males grab the females around the neck and hold on tightly, to prevent other males from scooping out their sperm. The other part of this is males have two locations for sperm. One in their tail, and the other in their thorax. The male transfers the sperm to the thorax area, and this is where the female reaches up to grab the sperm for herself. Watching this summer as the dragonflies roamed crex, I saw multiple examples of second males just waiting for the first male to lose grip on the female. In the past, I have seen examples of three dragonflies gripped, and now that I know about the sperm scooping/thorax sperm holding area, it makes perfect sense, that the 2nd male (in a trio of three) is hoping the female connects with his thorax in her reaching, rather than the assumption the marks on male dragonfly necks is homosexual dragonfly activity.
